A hair-raising situation occurred on the morning of March 29 this year when NASA scientists working on the Fermi Gamma-ray Space Telescope project discovered that their spacecraft was just days away from hitting the Soviet Cosmos 1805.
According to a report released Wednesday by NASA, scientists revealed how one of their spacecraft came within a few hundred feet of a catastrophic collision with a defunct Soviet-era spy satellite last month. Fermi was launched into orbit in June 2008 from Cape Canaveral Air Force Station aboard a Delta II 7920-H Rocket.
The NASA craft, the Fermi Gamma-ray Space Telescope, was on the same trajectory as Cosmos 1805 - and the two craft were closing at a combined speed of 27,000 miles per hour. On the morning of March 29 this year, NASA scientist Julie McEnery received an email warning her of the approaching collision, which would have resulted in an explosion releasing the equivalent of energy from two and a half tons of high explosive.
"My immediate reaction was, 'Whoa, this is different from anything we've seen before!'" McEnery said.
Although the forecast indicated a close call, satellite operators have learned the hard way that they can't be too careful. The uncertainties in predicting spacecraft positions a week into the future can be much larger than the distances forecast for their closest approach.
Though Fermi was expected to miss Cosmos by several-hundred feet, NASA scientists knew from experience that forecasting spacecraft positions a week in advance isn't an exact science. For example, Iridium 33 and Cosmos 2251 collided in 2009 even though they were predicted to miss each other by approximately 1,900 feet. This was the first known satellite-to-satellite collision.
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